Cathode ray tube faceplate formed of graded index laminated plates

ABSTRACT

A transparent body of plate form is caused to have refractive index distribution conforming approximately to the equation nr no (1 - ar2), where no is the refractive index in a central plane of the body parallel to its flat surfaces, nr is the refractive index at a distance r from the central plane, and a is a constant, whereby light or light pattern constituting an image introduced into the body through an edge surface is conducted through the body to the opposite edge surface from which the light or image is directed out.

,6 a- 1" {J A uulwu ma 5}, j, a 1151 3,657,586 Matsushita et al. 7 i I[451 Apr. 18, 1972 54 CATHODE RAY TUBE FACEPLATE 3,083,123 3/1963 Navias..350/l75 GN UX 1 Schulz 1 X 3,434,774 3/1969 Miller 350/96 WG LAMINATEDPLATES 2,740,954 4/1956 1616mm ..350/l67 x [72] Inventors: KazuoMatsushita, Nishinomiya-shi; Ken OTHER PUBLICATIONS Koizumi, ltam1-sh1;l-lidetoshi Togo, Itam1- shi; Hajime Kimura, ltami-shi, all of JapanM1ller Artlcle in Bell System Techmcal Journal Vol. 44 No. 9 Nov.l965pp.2,0l72,030 Asslgneer Nippon Selfoc Kabushlkl Kalsha, y Kawakamiet al. Article in Proceedings of the IEEE Dec. 1965 to, Japan pp. 2,148and 2,149 .[22] Filed Aug 19 1969 R. W. Wood Physical Optics 2nd EditionPublished 1911 pp.

86-91 [2]] Appl. No.: 851,398

Primary Examiner-David H. Rubin Attorney-Robert E. Burns and Emmanuel J.Lobato [30] Foreign Application Priority Data Aug. 21, I968 lapan..43/60096 [57] ABSTRACT A transparent body of plate'form is caused tohave refractive [52] US. Cl ..3l3/92 LF, 350/96 R, 350/96 B, indexdistribution conforming approximately to the equation 350/175 GN n, n (1111 where n, is the refractive index in a central 5 Int noun 1 021 5 4plane of the body parallel to its flat surfaces, n, is the refracss 1Field of Search ..350/96, 96 B, 167, 175 GN; tive index at a distance rfrom the Central Plane, and a is a 9911- 313/92 stant, whereby light orlight pattern constituting an image introduced into the body through anedge surface is conducted through the body to the opposite edge surfacefrom which the [56] References Cited light or image is directed out.

UNlTEDSTATESPATENTS 2C] 7D F a m a 1 1,882,829 10/1932 Hall ..350/l67 uxs gums PAIENTEDAPR 18 1972 SHEET 10F 2 7 FIG.

FIG. 6

EFRACTIVE max BACKGROUND OF THE INVENTION This invention relatesgenerally to light-conducting structures and more particularly to a newlight-conducting structure consisting of a transparent material having arefractive index distribution in a one-dimensional direction.

Heretofore, a light-conducting structure of fibre form or cylindricalform comprising a core of a transparent light-conducting substance of arelatively high refractive index and a covering layer of alight-conducting substance of a relatively low refractive index has beenknown. Incident light introduced through one end of the core of such alight-conducting structure at an angle greater then the reflectioncritical angle of the interface between the core and covering layer iscaused to propagate through the core as it is repeatedly reflected bythe interface.

A light-conducting structure of this known clad type is utilized merelyfor conducting light owing to its reflection and cannot conduct visualimages, having no resolving power. According to one known proposal forconducting images, the above-mentioned light-conducting structure ismade in the form of a bundle of fibres, the relative positions of saidfibers at the light incident surfaces and at the light exiting surfacesthereof are aligned, and the light and dark parts of the image areallocated d to the fibrous light-conducting structure thereby topropagate the image.

In an image-conducting structure of this character, the definition ofthe image thus propagated and the resolving power are improved withdecrease in the thickness of the fibrous light-conducting structures orin the thickness of the covering layer. However, the fusion bonding of acovering layer on a thin core or the alignment of the relative positionsof the light incident and exit parts of thin fibrous light-conductingstructures and the fusion bonding of the bundle of these structures aredifficult and require much labor Furthermore, it is even more difficultto fabricate a large bundle of these image-conducting structures.Consequently, the size of images which can be thus propagated islimited.

According to one known proposal for conducting large images by means oflight-conducting structures of the abovedescribed character, theobjective image is reduced in size by a lens system and introduced intothe incident part and is enlarged again at the exit part to beextracted. Since the thickness of the light-conducting structures islimited, however, it has not been possible to achieve sufficient imagedefinition, that is, resolving power.

SUMMARY OF THE INVENTION It is an object of the present invention toutilize advantageously certain findings we have made to provide alightconducting structure having no covering layer and having resolvingpower in a one-dimensional direction, particularly a light-conductingstructure suitable for use in conducting light having a propagationcomponent in a two-dimensional direction, that is, light whichpropagates within one plane.

According to the present invention is one aspect thereof, brieflysummarized, there is provided a light-conducting structure composed ofat least one transparent structure having a refractive index n, in acentral plane passing through the central part thereof and a refractiveindex n, at a distance r from the central plane, the refractive indexdistribution being such as to satisfy substantially the equation n,= n,(l ar"), where a is a positive constant, whereby light introduced intothe transparent structure through a first end surface is conductedtherethrough to be directed out of an end surface opposite the first endsurface.

According to the present invention in another aspect thereof, there isprovided a composite combination formed by larriinately combining aplurality of transparent structures each having the above describedcharacter with or without thin light-absorbing layers interposed betweenrespective pairs of adjacent structures.

The nature, principle, details, and utility of the invention will bemore clearly apparent from the following detailed description withrespect to a preferred embodiment of the invention when read inconjunction with the accompanying drawing, in which the same orequivalent members are designated by the same reference numerals andcharacters.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a perspective view showing a basic example of alight-conducting structure according to the invention;

FIG. 2 is a graphical representation indicating the refractive indexdistribution in the axial direction designated as X in a sectional planetaken perpendicularly to the central plane 2 at any position of thelight-conducting structure shown in FIG. 1;

FIG. 3 is a perspective view of an example of a face plate of acathode-ray tube in which a light-conducting structure of the inventionis used;

FIG. 4(A)(B) are diagrammatic views indicating a facsimile apparatus inwhich the faceplate shown in FIG. 3 is used.

FIG. 5 is a perspective view showing an example of a pipeshapedlight-conducting structure of the invention; and

FIG. 6 is a characteristic graph showing internal refractive indexdistribution of the light-conducting structure illustrated in FIG. 5.

DETAILED DESCRIPTION As shown in FIG. 1,'the light-conducting structureof the invention is composed of a transparent structure 1 having twoopposite side surfaces 3 and 3a, two opposite end surfaces 5 and 6, andtwo other opposite end surfaces 7 and 8. The refractive index of thistransparent structure 1 decreases in accordance with curve 4 asindicated in FIG. 2 from a plane 2 passing through the centre of thetransparent structure toward the outer surfaces 3 and 3a thereof, thatis, in the outward directions along axis X from the central plane 2. Inthe use of this transparent structure 1, light is introduced thcreintothrough one end surface such as 5 or 7 and light is led out through theopposite end surface 6 or 8.

A light-conducting fibre in which the refractive index decreasesprogressively from, the inner part toward the outer part thereof hasbeen proposed (as disclosed in, for example, the Proceedings of theIEEE, Vol. 53, p. 2148-p. 2149, Dec. 1965). The present invention makespossible the provision of a light-conducting structure having arefractive index distribution which can be readily manufactured inactual practice.

More specifically, the present invention is based on a phenomenonwhereby, when incident light is introduced at a specific angle into oneend surface of a transparent'structure of a nature such that therefractive index thereof decreases from a plane passing through thecentral part thereof toward two opposite surfaces thereof perpendicularto the end surface, the light advancing through its propagation path iscontinually curved toward the direction in which the refractive indexincreases and can be directed out of the structure through the oppositeend surface. The success of the present invention is a confirmation ofthe validity of this principle.

We have found further that a preferable refractive index distribution issuch that the refractive index n, at any point within the structureconforms to the following equation.

n,=n,,(1ar where: n is the refractive index at the central plane;

r denotes the distance of the above-mentioned point from the centralplane; and

a is a positive constant.

We have found that a light-conducting structure having a refractiveindex distribution of this character is capable of propagating in thedirection of the Y or Z axis the light intensity variation (bright anddark) in the direction of the refractive index distribution, that is,the X direction as indicated in FIG. 1. That is, the principle of thislight-conducting structure is similar to that of the so-called gas lens,whereby this structure has a lens effect and has resolving powerin thedirection ofthe refractive. index distribution.

We have found further that while this light-conducting structure can becurved if it is made thin, light within the structure does not escapefrom the lateral sides thereof when the structure is curved within acertain limit in the direction of the refractive index distribution.This limit to the possible degree of curvature is determined by therefractive index distribution and increases with increase in thegradient of the refractive index.

Since the light-conducting structure of the invention has a lightfocusing effect in a one-dimensional direction, it is particularlysuitable for use in conducting light having traveling components in oneand the same plane.

In a light-conducting structure such as shown in FIG. 1 in which itslength along the axis 2 is longer than that along the axis y, when alight-beam is transmitted through the interior of said structure alongsaid axis z, the transmitting light-beam is gradually expanded towardaxis y and a part of the transmitting light is made to collide againstside surfaces 5 and 6, whereby transmission of the light-beam isdisturbed. This disadvantageous fact can be eliminated by constructingthe lightconducting structure so that in a sectional plane perpendicularto center plane of the structure its centerline forms a close curve,whereby the light-beam cannot collide against the side surfaces in theinterior of the structure, thus causing an eff cient transmission of thelight-beam.

By suitably selecting the length of the conducting structure, it ispossible to obtain at the outlet directly, without change, variation oflight intensity at the incident light inlet in the direction of therefractive index distribution (i.e., the direction of axis X in FIG. 1).When the length t of a lightconducting structure having theabove-described refractive index distribution, which length t is in thedirection of travel of the light to be conducted, is expressable bywhere n is an integer, the variation of light intensity of the lightincident surface of the structure in the direction of the refractiveindex distribution can be conducted directly to the lightexitingsurface. Furthermore, by cutting this light-conducting structure to asuitable length, a lens having both end surfaces flat an equivalent to aconventional cylindrical lens can be ob tained.

Furthermore, in still another aspect of the invention, it is possible toform a composite structure consisting of a surfaceto-surface laminationin the thickness direction of a plurality of transparent plate-shapestructures each having the abovedescribed refractive index distributionin the thickness direction. By introducing incident light at a certainangle into one end surface of this composite structure, it is possibleto extract this light from the opposite end surface.

A structure resulting when two end parts of this composite structure arealigned is equivalent to a structure formed by aligning in a row a largenumber of conventional cylindrical lenses and can be rendered into alenticular lens for reproducing three-dimensional images ofthree-dimensional photography which has resolving power in the directionof the refractive index distribution.

Furthermore, when the length t of this composite structure in the lighttravel direction is representable by where n is an integer, thevariation of light intensity in the direction of refractive indexdistribution of one end surface which is the light incident surface canbe conducted to the opposite end surface which is the light-exitingsurface. Accordingly, this composite structure is optional for use asthe face plate of a cathode-ray tube for large-size facsimiles. Whenthis structure is thus used, light which enters and advances with alarge incidence angle at the incidence surface of each transparent platestructure having the above-described refractive index distributionenters into other adjacent transparent plate structures, whereby lighttransmission is liable to be disturbed. For the purpose of avoiding thisdisturbance light-absorbing layers are interposed between adjacent platestructures constituting the light-conducting structure.

For the transparent structure having the refractive index distributionaccording to the invention, a glass or a synthetic resin is suitable. Inthe case of glass, it is possible to cause it to have theabove-described refractive index distribution by the ion-exchange methodthe provision of which is an object of US. Pat. application Ser. No.806,368 filed Mar. 12, 1969.

More specifically, in one instance of practice, a glass plate of athickness of 1 mm. composed of 56% of SiO:, 14% of Na O, 20% of T1 0,and 10% of PbO, all percentages being by weight, was steeped for aspecific time in a potassium nitrate bath maintained at a hightemperature. The glass plate was then taken out of the bath, and thesurrounding edges of the plate were cut off.

As a result, a glass plate having a refractive index n at the centralpart thereof of 1.56 and a refractive index at the outer surface thereofof 1.48 and having a refractive index distribution such as to satisfythe relationship n,- n (I ar a 0.21 mm, in the thickness direction wasobtained. When parallel-ray light was introduced at a certain incidenceangle through an end or edge surface of this glass plate, it waspossible to extract this light at the opposite end surface.

From this glass plate, a number of light-conductin ieces 11 each of awidth of 3 mm. and a length t 2 rrl{2 ri 9.8 mm. were prepared. Thesepieces 11 were fusion bo ded with light absorbing layers 12 interposedtherebetween so that the surfaces of low refractive index faced eachother, that it, so that the light-conducting pieces 11 had refractiveindex distributions in the X-axis direction, thereby to form a faceplate13 as shown in FIG. 3.

One end surface 14 of this face plate was covered with a coating of aphosphorescent substance 15, and the opposite end surface 16 was coatedwith a light absorbing material 18, a slit 17 being left to permitpassage of light through the central part of the face plate in theZ-axis direction.

A face plate 13 fabricated in the above-described manner was used in acathode-ray tube 19 for a facsimile apparatus as indicated in FIG. 4(A).In this apparatus, an electron beam 21 emitted by the electron gun 20 ofthe cathode-ray tube 19 scans the phosphorescent body 15 on the oppositeside from the slit 17 of the face plate.

The phosphorescent body 15 luminesces in accordance with the intensityof the electron beam 21 by which it is scanned, and only the portion ofthe light passing through the slit 17 is projected onto thephotosensitive recording medium (paper) 23. That is, light which has apropagation component in the Z- axis direction is absorbed by thelight-absorbing material 18, while light traveling in the direction ofthe bonded surfaces 22 is absorbed by the light absorbing material 12.

As shown in FIG. 4(B), the light-beams emitted from a point P of thephosphorescent body 15 propagate through the interior of thelight-conducting pieces 11 as shown by arrows and these light-beams areconcentrated at a point Q the position of which corresponds to that ofthe point P. If the point P transfers toward the X direction, the pointQ also transfers in accordance with the transference of the point P.

The recording paper 23 being scanned by the electron beam 21 isprogressively taken up on a drum 24 in accordance with the scanningspeed of the electron beam, and the patterns of light intensityvariation in the X-axis direction produced successively by the electronbeam are recorded on the recording paper, whereby images or charactersare reproduced on the recording paper 23.

Thus since the light-conducting structure according to the invention hasresolving power in the X-axis (FIG. 3) direction, it is possible to usea light-conducting structure of plate shape having a great thickness inthe X-axis direction. Accordingly, the difiiculty in the production ofconventional face plates of cathode ray tubes of bundlinglight-conducting structures of fiber form and aligning thelight-incident inlets and light-exiting outlets thereof is overcome.

The present invention therefore facilitates the fabrication of faceplates for cathode-ray tubes and makes possible the production oflarge-size face plates. The invention, moreover,

makes possible reproduction on recording paper of images andinscriptions of high definition.

EXAMPLE A hollow glass consisting of 20% of T1 0, of PhD, 14% of Na Oand 56% of SiO by weight respectively, and having outer diameter ofabout 3mm and inner diameter of 1 mm, inner and outer circles of thesectional surface of said pipe being concentric, was immersed in a bathof potassium nitrate or 480 C. for 48 hours while maintaining the meltof the potassium nitrate in the hollow part of the pipe, said glass pipewas washed with hot water after said immersion, and then both ends ofthe glass pipe were cut off, whereby a hollow glass pipe 25 such asshown in FIG. 5 was obtained, refractive index of said glass pipe 25being 1.57 at about center part 27 of the pipe wall 26 and 1.54 at outersurface 28 and inner surface 29, and the refractive index N of the pipebeing decreased from said center part 27 toward outer and inner surfacesin proportion to square of the distance from the center part as shown inFIG. 6. When a light is made to enter, at an angle, into one end face 30of the glass pipe 25 having the abovementioned refractive indexdistribution, the incident light is transmitted toward the other endface 31 while being always refracted toward parts of larger refractiveindex 27 without collision with the outer and inner surfaces 28 and 29,and the light reached said end face 31 is emitted, at an angle, out ofthis end face. As such light-conducting structure as described above maybe formed as a circular hollow pipe, in which its outer or innerdiameter is gradually varied or rate of decrease of the refractive indexat a sectional area is varied. Furthermore, a circular hollow pipe,inner and outer circles of which are not concentric, or a hollow pipehaving any polygonshaped sectional area may be used with same effect.

We claim:

1. A cathode-ray tube faceplate comprising a plurality of likeplate-shaped transparent bodies each having a center plane, an entrancesurface and an exit surface both disposed transverse to said centerplane and opposite side surfaces extending between said entrance surfaceand said exit surface and parallel to said center plane, each said bodyhaving a refractive index distribution in a cross section in a planeperpendicular to said center plane which substantially satisfies theequation:

n, n (1 ar) wherein n represents the refractive index at said centerplane, n, represents the refractive index at a point in the plane ofsaid cross section spaced a distance r from said center plane, and a isa positive constant, said bodies being laminated with one another sidesurface to side surface into a combined structure with a thin lightabsorbing layer interposed between adjacent side faces of saidtransparent bodies, said center planes of said bodies being parallel toone another and said entrance surfaces and exit surfaces constitutingsmooth continuous inner and outer surfaces respectively of saidfaceplate and being uniformly spaced from one another at a distancesubstantially equal to 2m'r 2a where n represents a positive integer, acoating of a phosp orescent substance on said inner surface of saidfaceplate activatable to produce an image which is transmitted to saidouter surface as an erect image having the same size as that produced onthe inner surface of the faceplate by said coating and masking means forlimiting the erect image produced on said outer surface to a narrowstrip extending perpendicular to said center planes of said transparentbodies. 2. A cathode-ray tube faceplate according to claim 1, in whichsaid masking means comprises a layer of light-absorbing material formedon said outer surface and having a central slit extending perpendicularto said center planes of said transparent bodies for the of thefaceplate.

passage of light through the central part-

1. A cathode-ray tube faceplate comprising a plurality of likeplate-shaped transparent bodies each having a center plane, an entrancesurface and an exit surface both disposed transverse to said centerplane and opposite side surfaces extending between said entrance surfaceand said exit surface and parallel to said center plane, each said bodyhaving a refractive index distribution in a cross section in a planeperpendicular to said center plane which substantially satisfies theequation: nr no (1 - ar2) wherein no represents the refractive index atsaid center plane, nr represents the refractive index at a point in theplane of said cross section spaced a distance r from said center plane,and a is a positive constant, said bodies being laminated with oneanother side surface to side surface into a combined structure with athin light absorbing layer interposed between adjacent side faces ofsaid transparent bodies, said center planes of said bodies beingparallel to one another and said entrance surfaces and exit surfacesconstituting smooth continuous inner and outer surfaces respectively ofsaid faceplate and being uniformly spaced from one another at a distancesubstantially equal to 2n pi 1 square root 2a where n represents apositive integer, a coating of a phosphorescent substance on said innersurface of said faceplate activatable to produce an image which istransmitted to said outer surface as an erect image having the same sizeas that produced on the inner surface of the faceplate by said coatingand masking means for limiting the erect image produced on said outersurface to a narrow strip extending perpendicular to said center planesof said transparent bodies.
 2. A cathode-ray tube faceplate according toclaim 1, in which said masking means comprises a layer oflight-absorbing material formed on said outer surface and having acentral slit extending perpendicular to said center planes of saidtransparent bodies for the passage of light through the central part ofthe faceplate.